When the blood vessels damaged in clinical, such as thrombosis, vascular stenosis etc., the autologous saphenous vein graft, vascular graft substitute made by synthetic materials are usually used as vascular graft substitutes mostly during the surgery. However, there are some disadvantages of the above vascular graft substitute, such as the limitation of lumen size, and the stability is low and the thrombosis is easily caused, restenosis and severe inflammatory immune is easily occurred again.
The vascular graft substitute used in clinical can be divided into four categories:
(1) Autologous grafts: this is the best choice for clinical vascular graft substitutes, which is obtained from the section of saphenous vein or artery from the patient's chest as a vascular graft substitutes. There is disadvantage that the patients needed this kind of surgery, who usually have preexisting diabetes, hypertension and other related diseases. Therefore, the blood vessels are not healthy and with many existing problems, such as varicose veins, arteriovenous peeling and other conditions. Furthermore, the vein may be achieved from the previous vascular surgery vascular which is not appropriate for use. In addition, if the arterial vessel is replaced by vein, short restenosis rate is very high after transplantation of the vascular graft substitutes due to the different structure and function of blood vessels, therefore, the blood vessel obtained from patients is not quite suitable. Furthermore, the obtained blood vessel lumen size are larger than most coronary caliber (the lumen of coronary arterial is typically less than 4 mm), that would increase the surgical procedure more difficulty during implementing joining. (Reference from: Thomas O. D. et al., 2003)
(2) Allografts, xenografts: other people's blood vessels, umbilical cord, or animal bodies' blood vessels (cattle, pigs, dogs, etc. . . . ) are as vascular graft substitutes after the removal process of cells and cross-linking process. The disadvantage of this type vascular graft substitutes is that the severe inflammation and infection autoimmune response would occur in a short term after transplantation, and the aneurysm would be deteriorate and metastatic phenomenon would occur. (Reference from: Thomas O. D. et al., 2003)
(3) Synthesis of polymer materials: non-biodegradable (nylon, Teflon, Orlon, Dacron, polyethylene (PE), silicon, poly (tetrafluoroethylene) (e-PTFE) and polyurethane (PU) . . . etc.) (Greisler H. P., 1991) and biodegradable (poly-L-lactic acid (PLLA), poly (lactic-co-glycolic acid) (PLGA)) are mainly used as the synthetic material of vascular graft substitutes (Chu F L et al., 1999). The disadvantage of this type vascular graft substitutes is that a non-degradable synthetic material is widely used in large diameter (usually greater than 4 mm diameter vessels), the blood vessel region of high velocity vascular graft substitute. When the vascular graft substitute is used in small-diameter (less than 4 mm) blood vessel region, the vascular restenosis and thrombosis would easily occur due to the material accumulation and excessive intimal proliferation in engaged position. (O'Donnell T F et al., 1984). When the decomposable polymer synthetic materials are used, the product of degradation after transplantation would cause the local peracids of surrounding tissue, and sometimes the chronic inflammation would be caused.
(4) Artificial blood vessels of natural polymer material: vascular graft substitutes are made from the materials contains collagen, animal gelatin, fibrin glue, chitin, hyaluronic acid . . . etc The disadvantage of the vascular graft substitutes made from natural polymeric materials is that there is problem of insufficient mechanical strength and the degradation time is too fast to maintain the structure until autologous cells recover completely. (Reference from: Weinberg C B et al, 1986. Grassi E D et al, 2003.).
In clinical, the need of vascular graft substitutes with high stability, low cost, no limitation of the vessel lumen and high biocompatibility, to be a vascular graft substitutes for damaged blood vessels is urgent.